1. Field of the Invention
The present invention pertains to telecommunications, and particularly to telecommunications operations wherein plural transport channels, each having potential plural transport formats, are multiplexed for transmission.
2. Related Art and Other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (xe2x80x9ccellularxe2x80x9d telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which is in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a wideband code division multiple access (W-CDMA) system.
The UTRAN uses the Open Systems Interconnection (OSI) reference model. The Open Systems Interconnection (OSI) reference model describes how information from a software application in one computer or telecommunications node moves through a network medium to a software application in another computer or node. The OSI reference model is a conceptual model composed of seven layers, each specifying particular network functions. Each layer is reasonably self-contained, so that the tasks assigned to each layer can be implemented independently. The upper layers of the OSI model deal with application issues and generally are implemented only in software. The highest layer, i.e., the application layer, is closest to the end user. Both users and application-layer processes interact with software applications that contain a communications component. The term upper layer is sometimes used to refer to any layer above another layer in the OSI model. The lower layers of the OSI model handle data transport issues. The physical layer and data-link layer are implemented in hardware and software. The other lower layers generally are implemented only in software. The lowest layer, the physical layer or layer 1, is closest to the physical network medium (the network cabling, for example, and is responsible for actually placing information on the medium).
In telephony, particular mobile telecommunications such as the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN), plural transport channels can be multiplexed over an interface [comprising, e.g., a transmission line or radio frequency(s)]. Assume, for example, that I number of transport channels TrCHi, i=1, 2, . . . , I, are multiplexed, and that each TrCHi has Li number of transport formats. Thus, if each transport channel TrCHi has a format indication TFIi, the format indication TFIi can take Li values, TFIi, {0,1,2,K,Lixe2x88x921}. If all combinations of transport formats are allowed, the number of transport format combinations (TFCs) will be C=L1xc3x97L2xc3x97 . . . xc3x97LI. The number of transport format combinations can become a rather significant number, even with only a few transport channels being multiplexed. In reality, only a subset of all the C TFCs are used. For example, assume a UEP AMR speech service with three transport channels for the three protection classes. AMR has 9 different rates (including DTX), so only 9 TFCs are used. However, in this scenario, C computes to 9xc3x978xc3x973=216 combinations. Similar problems, e.g., a high number of combinations, can arise when considering other service combinations.
Layer 1 of an OSI reference model telecommunications system allocates signaling for a large number of transport format combinations. A Transport Format Combination Indicator (TFCI) informs a receiver of the transport format combination of the CCTrCHs. A current TFCI mapping rule is established in Technical Specification 3GPP TS 25.212 (xe2x80x9c3GPPxe2x80x9d refers to a project known as the Third Generation Partnership Project (3GPP), which has undertaken to evolve further the UTRAN and GSM-based radio access network technologies). As soon as the TFCI is detected, the transport format combination, and hence the individual transport channel""s transport formats, are known by the receiver, so that the receiver can perform decoding of the transport channels.
As it turns out, many transport format combinations are not utilized. Allocating Layer 1 signalling (TFCI) for a large number of transport format combinations, many of which are not used, leads to at least two problems. The first problem is that there may not be enough available TFCI words (64 or 1024). The second problem is that the performance of the TFCI detection depends on how many TFCI code words are in use. There is a significant difference detecting 8 code words out of 64 possible or detecting 64 code words out of 64 possible. Moreover, using a 2xc3x97(15,5) code to handle up to 1024 TFCI code words has much worse performance than the 1xc3x97(30,6) code that handles up to 64 TFCI code words. Hence, from a performance point of view, one should not allocate TFCI for combinations that are not used.
The current TFCI mapping rule defined in TS 25.212 does not take into account that not all transport format combinations are possible. Hence, the allocation used in used in the TS 25.212 specification can suffer from wasting the TFCI code words.
What is needed, therefore, and an object of the present invention, is an efficient and unambiguous way of mapping each allowed transport format combination (TFC) to a certain Transport Format Combination Indicator (TFCI).
A Calculated Transport Format Combination (CTFC) provides efficient signalling of transport format combinations to be assigned TFCI values. A sequence of CTFCs is signalled from higher layers to Node B and the user equipment unit (UE), where each CTFC in order is allocated a TFCI value. From the CTFC both Node B and the user equipment unit (UE) can determine the exact transport format combinations the TFCI values (used to communicate between Node B and UE) represent.
For I number of transport channels that are included in the transport format combination, with each transport channel TrCHi, I=1, 2, . . . , I, having Li transport formats, i.e. the transport format indicator TFIi can take Li values, TFIi0 {0, 1, 2, . . . , Lixe2x88x921}. Let TFC(TFI1, TFI2, . . . , TFII) be the transport format combination for which TrCH1 has transport format TFI1, TrCH2 has transport format TFI2, etc. The corresponding CTFC(TFI1, TFI2, . . . , TFI1) is then computed as:       CTFC    ⁡          (                        TFI          1                ,                  TFI          2                ,        K        ,                  TFI          I                    )        =            ∑              i        =        1            I        ⁢                  TFI        i            ·                        P          i                .            
wherein             P      i        =                  ∏                  j          =          0                          i          -          1                    ⁢              xe2x80x83            ⁢              L        j              ,
where i=1, 2, . . . , I, and L0=1.